Thermal Conversion of Solid Wastes and Biomass - ACS Publications

43 Development of a Solid Waste Disposal System with Pyrolysis and Melting Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 29, 2018 | https://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch043

M. ONOZAWA

Solid Waste Melting System Project Office, Plant and Machinery Division, Nippon Steel Corporation, Nakabaru 46-59, Tobata- Ku, Kitakyushu City, Fukuoka Prefecture 050, Japan

1.

Introduction

Recently in Japan, the improvement in living standards has given rise to an increase in the quantity and a diversification of the properties of wastes from households. This has become an increasingly important problem for local governments. At present, the greater part of such wastes are being disposed of by burning in stoker incinerators. But an increase in the amounts of difficult-to-burn or incombustible wastes such as plastics, glass bottles and cans, which started in about 1965, has made the present incineration method increasingly ineffective. Hence, ways to overcome the limits of the present method are being investigated. Taking an interest in this field, Nippon Steel Corporation in 1972 started studying a pyrolysis and melting method using a shaft furnace for the disposing of non-industrial wastes. Since 1974, experiments have been carried out at a 20-ton-per-day pilot plant built in Tobata, Kitakyushu. The object of the fusion-thermal composition method, is to recover energy from inflammable gas; render product ashes into slags at high temperatures, thus making heavy metals, if any, eludible; decrease the volume of the end products; and process the product gas so that less HCl and NOx are discharged into the atmosphere. In an attempt to reduce secondary pollution and protect the incinerators, the Tokyo Metropolitan Government, since 1973, has been asking households to separate some items from ordinary wastes before they are put out for collection. The items to be separately collected include those which cannot be burned, such as metals, glass and ceramics, and those which should not be burned, such as plastics, rubber, hides and leather. These items are buried in reclaimed lands, unprocessed. After inspecting the Tobata pilot plant, the Bureau of Public Cleansing of the Tokyo Metropolitan Government decided to perform experiments to ascertain the applicability of this system to the processing of the classified refuse described above. In response, 0-8412-0565-5/80/47-130-603$05.00/0 © 1980 American Chemical Society Jones and Radding; Thermal Conversion of Solid Wastes and Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 29, 2018 | https://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch043

604

THERMAL

CONVERSION

OF

SOLID

WASTES

AND

BIOMASS

Nippon S t e e l , i n conjunction with the P l a s t i c Waste Management I n s t i t u t e , o f f e r e d the government use of an experimental p l a n t , with a capacity of 40 tons per day. The Government, i n t u r n , subcontracted the performance of the experiments to Nippon S t e e l . The experiments were s t a r t e d i n January 1978, and completed i n August 1979, y i e l d i n g almost a l l the expected r e s u l t s . Taking advantage of the r e s u l t s obtained from these t e s t p l a n t s , Nippon S t e e l i s c o n s t r u c t i n g a 100-ton-per-day plant (50ton-per-day u n i t χ 2) i n Kamaishi and a 450-ton-per-day p l a n t (150-ton-per-day u n i t χ 3) i n I b a r a g i . 2.

Outline of the System

This waste d i s p o s a l system centers upon a melting furnace. The system can be d i v i d e d i n t o two main types, according to how the gas generated i n the furnace i s t r e a t e d . Figure 1 i s a schematic flow sheet of the type of system that recovers the inflammable gas; t h i s system i s used i n Tokyo f o r p r o c e s s i n g the c l a s s i f i e d refuse. Figure 2 i s a schematic flow sheet of the d i r e c t combustion system. For e f f e c t i v e burning of refuse, coke must be added as a supplementary f u e l and limestone as a f l u x . To melt the s l a g at high temperatures, preheated, oxygen-enriched a i r i s blown i n t o the furnace. A c c o r d i n g l y , i r o n , g l a s s , ceramics and the l i k e contained i n the refuse are discharged from the furnace i n a molten s t a t e . In the gas recovery system, the dust and t a r from the wet scrubber may be returned to the furnace f o r f u r t h e r docomposition. The dust contains some heavy metals as z i n c and lead and a l k a l i c h l o r i d e s that may v a p o r i z e i n the furnace, so, not a l l dust can be returned. At present i n Tokyo, t h e r e f o r e , a c e r t a i n p o r t i o n of the dust and thickener l i q u i d i s processed i n a r o t a r y k i l n . Figure 3 shows the m e l t i n g furnace that forms the core of t h i s system. Refuse i s h o i s t e d from a storage p i t to the furnace top, and dumped i n t o the shaft furnace. Two s e a l v a l v e s attached to the charging hopper open a l t e r n a t e l y to prevent the leakage of gas r e s u l t i n g from thermal decomposition. Descending through the furnace, the charged refuse meets the ascending high-temperature gas. Any moisture contained i n the refuse evaporates and com b u s t i b l e s are g a s i f i e d . In f r o n t of the tuyeres supplying the oxygen-enriched a i r , coke and char, which i s p y r o l y s i s product, are burned at high temperatures. The ash and i r o n contained i n the waste melt i n t o s l a g and molten i r o n . When a c e r t a i n q u a n t i t y of these molten m a t e r i a l s has c o l l e c t e d i n the hearth, they are tapped out, then s o l i d i f i e d i n v e s s e l s . The molten substances may a l s o be dropped i n t o water j e t s to form granulated s l a g s . In the inflammable gas recovery system, the gas i s cleaned f i r s t by c o l l e c t i n g coarse dust with a dry dust c o l l e c t o r , then

Jones and Radding; Thermal Conversion of Solid Wastes and Biomass ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

605

Solid Waste Disposal with Pyrolysis and Melting

ONOZAWA

Classified Refuse 1,000 kg

Limestone 200 kg _]

Coke 80 kg

Heat _j Exchanger ;

3

A i r 570Nm /tR 70Nm /tR 0 30%

r

3


2

of a i r + 0 500°C 2

Shaft Melting Furnace

Dry Dust Collector

Wet Gas Cleaning Unit

F u e l Gas 900 Nm - d r y 1200 K c a l / Nm -dry 3

Thickener) Dust and Tar 100 kg Rotary K i l n

Slag 450 kg I r o n 100 kg Figure 1.

Ordinary Refuse 1,000 kg

Ash

Typical example of gas recovery system for classified refuse

Limestone 110 kg

Coke 80 kg Heat Exchanger

3

A i r 520Nm /tR 0 115Nm /tR Oo 35% 3

Steam

2

Preheating temp, of air + 0 250°C 2

Shaft Melting Furnace

Elec Dry Dust Combustric C o l l e c HH t i o n μ4 B o i l e r PH P r e tor Chamber cipita tor

• Dust 30 kg Slag Iron

200 kg 30 kg

Figure 2. Typical example of direct combustion system for ordinary refuse


THERMAL CONVERSION OF SOLID WASTES AND BIOMASS


606



43.

ONOZAWA

607


by e l i m i n a t i n g the f i n e r dust and a part of t a r by using a wet scrubber. Part of the c l e a n gas i s consumed i n hot stoves f o r the heating the oxygen enriched a i r that i s blown i n t o the furnace, while the r e s t i s s u p p l i e d as f u e l to b o i l e r s and other gas-spending f a c i l i t i e s . In the d i r e c t combustion system, the gas h e a v i l y laden with steam, dust and t a r i s burned i n the combustion chamber. P a r t of the gas i s used as an energy source f o r hot stoves, with the r e mainder being s u p p l i e d to a b o i l e r f o r heat recovery. Then, they are both cleaned by an e l e c t r i c p r e c i p i t a t o r , and discharged i n t o the atmosphere through an i n d u c t i o n fan. 3. 3.1.

Experimental

Procedures

Tobata P i l o t P l a n t

The Tobata p i l o t p l a n t has been conducting experiments s i n c e 1974. The gas processing system was of the inflammable gas r e covery type o r i g i n a l l y , but l a t e r modified to permit o p e r a t i o n on the d i r e c t combustion p r i n c i p l e , a l s o . At present, the system i s operated mostly u s i n g the l a t t e r method. Using t h i s p i l o t p l a n t , b a s i c , comparative s t u d i e s have been made on the furnace p r o f i l e , e f f e c t s of the p r o p e r t i e s of wastes and the oxygen c o n c e n t r a t i o n i n the b l a s t , the need f o r supplementary f u e l , and how to process the product gas. (1)

Refuse P r o p e r t i e s The refuse used f o r the experiments were the o r d i n a r y urban r e f u s e ( a l l - i n c l u s i v e ) c o l l e c t e d from Kitakyushu C i t y . Table I shows t h e i r usual p r o p e r t i e s . Table I. P r o p e r t i e s of Urban Refuse from Kitakyushu C i t y (On Wet B a s i s ; %)

Physical Properties

Combustibles

Chemical Properties

Moisture

59.6

48.2

Undesirable Combustibles 10.5

Incombustibles 29.9

Combustibles

Ash

33.2

Total 100.0 Total

18.6

(2)

100.0

Experimental Progress E i g h t thousand seven hundred tons of wastes were d i s posed of i n approximately 12,000 hours between November 1974 and June 1979. (3)

Experimental Conditions 1) B l a s t volume 560 ^ 1,200 Nm /hr 3


608

THERMAL

2)

CONVERSION OF SOLID WASTES AND

BIOMASS

Oxygen quantity ( i n a i r + enrichment) 160 ^ 250 Nm /hr Oxygen c o n c e n t r a t i o n 20.9% ( a i r ) ^ 36% A i r preheating temperature Ambient - 400°C Limestone 80^120 kg/ton of refuse 3

3) 4) 5)


By v a r y i n g the b l a s t volume, oxygen c o n c e n t r a t i o n , preheating temperature and other f a c t o r s , the optimum quantity of refuse charge, coke requirement and other c o n d i t i o n s f o r s t a b l e p l a n t o p e r a t i o n have been studied. 3.2.

Tokyo Test Plant

Experiments on the Tokyo Test Plant were s t a r t e d i n December 1977 and ended i n August 1979. Using mainly the aforementioned c l a s s i f i e d r e f u s e , t h i s p l a n t was operated continuously f o r a long time, i n order to r e c o n f i r m the requirements f o r s t a b l e operation, u t i l i t i e s requirements and p o l l u t i o n c o n t r o l - r e l a t e d f i g u r e s e s t a b l i s h e d by the Tobata p i l o t p l a n t as w e l l as to study the f e a s i b i l i t y of l a r g e r - s i z e p l a n t s scale-up. (1)

Refuse P r o p e r t i e s The p r o p e r t i e s of refuse processed by the Tokyo p l a n t shown i n Table I I d i f f e r e d widely from those of Kitakyushu.

Table I I .

P r o p e r t i e s of C l a s s i f i e d Refuse Treated at the Tokyo P l a n t (On Wet B a s i s ; %) Incombustibles

Physical Properties

Chemical Properties

Combustibles

Undesirable Combustibles

31.3

19.9

Moisture

Combustibles

Ash

Total

18.6

33.8

47.6

100.0

Glass & Ceramics 31.0

Metals 17.8

Total 100.0

(2)

Experimental Progress 16,319 tons of refuse were disposed of i n 9,400 hours between December 1977 and August 1979. (3)

Experimental Conditions 1) B l a s t volume 1,280 ^ 1,645 Nm /hr 2) Oxygen quantity ( i n a i r + enrichment) 380 ^ 400 Nm /hr 3) Oxygen c o n c e n t r a t i o n 23.2 ^ 36% 4) A i r preheating temperature 700°C 5) Limestone Approximately 200 kg/ton of refuse 3

3


43.

609


ONOZAWA

Experimentation was s t a r t e d with the oxygen c o n c e n t r a t i o n of 23.2% and coke consumption of 108 kg per ton of r e f u s e . Tests on v a r y i n g oxygen enrichment were a l s o made. Nitrogen gas was used f o r purging the inflammable gas, and cement f o r s o l i d i f y i n g the r e s i d u e . S u b s t a n t i a l l y the same experimental c o n d i t i o n s as at the Tobata p i l o t p l a n t were used, except f o r the higher a i r preheating temperature.


4. 4.1.

Performance Experimental Results Table I I I .

T y p i c a l Experimental Results Tobata P i l o t P l a n t Tokyo Test P l a n t C l a s s i f i e d Refuse Ordinary Refuse

Item A i r , Nm /hr Pure oxygen, Nm /hr Oxygen c o n c e n t r a t i o n , % Waste d i s p o s a l r a t e , t / h r Coke consumption, kg/trefuse Limestone consumption, kg/t-refuse Tapping r a t e , kg/t-refuse Product gas, Nm / t - r e f u s e Gas composition, % N CO C02 H 3

2

2

CH4

C H 2

4

400 80 30 0.8

^ ^ ^ ^

550 100 36 1.0

1,100 100 26 1.8

^ ^ % ^

1,350 140 30 2.1

70 ^ 80

65 ^ 85

100 ^ 120

190 ^ 210

200 ^ 300 1,000

430 ^ 550 1,020

47.3 21.3 18.8 10.3 1.6 0.7

48.9 23.7 14.2 9.4 2.2 1.6

Table I I I l i s t s the t y p i c a l experimental r e s u l t s obtained from the two p l a n t s . Within the range of the t e s t s , coke consumpt i o n g e n e r a l l y decreased with i n c r e a s i n g oxygen c o n c e n t r a t i o n . For the same oxygen c o n c e n t r a t i o n , the c l a s s i f i e d r e f u s e , d e s p i t e i t s markedly l a r g e r s l a g production, consumed l e s s coke than the ordinary urban r e f u s e . Though not f u l l y proved, t h i s i s thought to be due to the higher moisture content of the ordinary urban refuse. The d a i l y d i s p o s a l c a p a c i t y was 16 to 22 tons f o r the Tobata p i l o t p l a n t , and 45 to 50 tons f o r the Tokyo t e s t p l a n t . 4.2.

Products and Uses


610

THERMAL CONVERSION OF

SOLID WASTES AND

BIOMASS

Slag and Iron By slowly c o o l i n g the molten product i n a v e s s e l , s o l i d r o c k - l i k e s l a g and i r o n are o b t a i n a b l e . When cooled r a p i d l y i n water j e t s , both s l a g and i r o n become sandy. The i r o n can be made i n t o weights or used f o r some other a p p l i c a t i o n s . The s l a g may be used f o r reclamation. I t s use i n the c i v i l - e n g i n e e r ing f i e l d , at present, i s l i m i t e d to sub-base m a t e r i a l . The s l a g has the p r o p e r t i e s shown i n Table IV, f r e e from such problems as the e l u t i n g of heavy metals. Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 29, 2018 | https://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch043

(1)

Table IV. Si0 46.6

2

CaO

A1 0

34.5

9.13

2

Slag Composition

3

(%)

MgO

Na 0

K0 2

T-Fe

1.98

4.87

0.74

1.25

2

(2)

Product Gas Within the oxygen c o n c e n t r a t i o n range of 28 to 36% used i n the experiments, 800 to 1,100 Nm of gas (dry) were generated per ton of r e f u s e . This y i e l d s 1,100 to 1,400 kcal/Nm of energy ( d r y ) . The heating value of the gas increases with i n c r e a s i n g oxygen c o n c e n t r a t i o n i n the hot b l a s t . 3

4.3.

Environmental

3

P o l l u t i o n Data

(1)

Noxious Gases Table V l i s t s the a i r p o l l u t a n t s contained i n the exhaust gas from the systems. The values vary to some extent with the p r o p e r t i e s of the r e f u s e that i s processed. The HC1, NOx and SOx concentrations obtained from the inflammable gas r e covery and d i r e c t combustion methods are c o n s i d e r a b l y lower than t h e i r concentrations i n the conventional i n c i n e r a t o r method. The concentrations of HC1 are e s p e c i a l l y low i n the two NSC Systems. Table V.

A i r P o l l u t a n t s i n Exhaust Gas

System

(ppm)

HC1

NOx

Inflammable gas recovery system (Exhaust gas a f t e r burning recovered gas)

15

58

7

D i r e c t combustion system

36

58

16

(After correcting 0 (2)

2

SOx

c o n c e n t r a t i o n i n exhaust gas to

12%)

Drainage I f requested by the user, both systems can be


designed

43.

611


ONOZAWA

so that no water i s drained o u t s i d e the system. The inflammable gas recovery system cannot dispense with the r o t a r y k i l n shown i n F i g . 1, s i n c e the r e c i r c u l a t e d water i n i t c a r r i e s organic matter and heavy metals. (3)

Slag The s l a g i s so s t a b l e that no heavy metals are eluted.


(4)

Dust Both systems generate 30 to 50 kg of dust and/or ash per ton of r e f u s e . To prevent the e l u t i o n of heavy metals, they must not be dumped unless they are s o l i d i f i e d w i t h i n cement. Table VI shows the chemical composition of the dust from the d i r e c t combustion system.

Table VI.

5.

Chemical Composition of Dust from the D i r e c t Combustion System (%)

C

S

Cl

Κ

Na

Ca

Si

Al

Zn

Pb

2.07

1.23

1.43

1.18

2.71

2.00

8.65

4.32

0.75

0.19

A p p l i c a t i o n to P r a c t i c a l Use

The two commercial p l a n t s being constructed i n Kamaishi and I b a r a g i are of the d i r e c t combustion type. F i g u r e 4 shows a b a s i c flow sheet on which the two p l a n t s a r e designed. The f u e l gas generated i n the m e l t i n g furnace are burned, together with dust and t a r , i n the combustion chamber. Although a small p a r t of the burned high-temperature gas passes through the a i r preheater, the greater p a r t flows i n t o the b o i l e r where waste heat i s recovered. The r e - j o i n e d gas streams are cleaned by the e l e c t r i c p r e c i p i t a t o r , then discharged i n t o the atmosphere through the i n d u c t i o n fan. The dust c o l l e c t e d by the p r e c i p i t a t o r , i s subjected to the e l u t i o n - p r e v e n t i n g measure, then d i s charged o u t s i d e the system. In the Kamaishi p l a n t , which i s r a t h e r s m a l l , the b o i l e r i s replaced with a gas c o o l e r . In both p l a n t s , s l a g s are water-granulated. The Kamaishi p l a n t i s scheduled to begin o p e r a t i o n i n August 1979, and the I b a t a g i p l a n t i n February 1980. 6. 6.1.

Consideration Comparison of the Two Gas Processing Methods



(1) air curtain; (2) collection vehicle; (3) receiving gate; (4) refuse storage bin; (5) crane operating room; (6) refuse crane; (7) refuse charging hopper; (8) coke storage hopper; (9) limestone storage hopper; (10) double seal valves; (11) melting furnace; (12) slag granulation pit; (13) magnet separator; (14) slag storage hopper; (15) iron storage hopper; (16) direct combustion chamber; (17) hot stove; (18) waste heat boiler; (19) electric precipitator; (20) clean water tank; (21) water purifying unit; (22) boiler drum; (23) steam turbine; (24) generator; (25) heat exchanger; (26) concrete solidifying equipment; (27) combustion air fan; (28) induced draft fan; (29) pit for bulky wastes; (30) crusher; (31) stack

Figure 4. Processflowsheet

fbc» ©


3

> g

M

H

^ >

to

43.

ONOZAWA



Table VII·.

613

Comparison of Gas Processing Methods D i r e c t Combustion Method

Description

Inflammable Gas Recovery Method

Gas Processing

Though dust c o l l e c t o r i s simple, water and t a r processing systems are complex and r e q u i r e l a r g e amounts of space.

Gases e n t e r i n g b o i l e r and heat exchanger are h e a v i l y laden with dust. Measures to prevent dust t r o u b l e are needed. Dust c o l l e c t o r takes up much space.

A i r Preheating

High temperature i s attainable.

High temperature i s d i f f i c u l t to a t t a i n .

Operation

Complicated by process-j ing of dustladen water.

Environmental Pollution

Much lower i n SOx and HC1 than the i n c i n e r ators

Simple.

Lower i n HC1 and NOx than the i n c i n e r a t o r s , j but a l i t t l e higher i n SOx and HC1 than the gas recovery method. !

For l a c k of s u f f i c i e n t l y long o p e r a t i o n a l experience, Nippon S t e e l cannot yet say which of the two methods i s more advantageous. The d i r e c t combustion system i s adopted f o r the I b a r a g i and Kamaishi p l a n t s . Generally, the choice between the two c a l l s f o r very c a r e f u l c o n s i d e r a t i o n of v a r i o u s f a c t o r s p e c u l i a r to each p l a n t . ).2.

Process Economics

In respect to economics, the p y r o l y s i s and m e l t i n g waste d i s p o s a l system under d i s c u s s i o n has the f o l l o w i n g advantages over the stoker i n c i n e r a t o r s that are most widely used i n Japan: (1) The NSC system i s capable of processing r e f u s e that are unsuited f o r burning or incombustible, and cannot be processed by the stoker i n c i n e r a t o r s . (2) There are few a i r p o l l u t a n t s emitted i n the NSC system, e s p e c i a l l y low are HC1 emissions. (3)

Whereas the ash from the stoker i n c i n e r a t o r s i n v o l v e



614

THERMAL

CONVERSION

O F SOLID W A S T E S

A N D BIOMASS

the r i s k of e l u t i n g organic matter and heavy metals, the s l a g from the NSC system i s p e r f e c t l y s t a b l e . When b u r i e d i n the reclaimed land, the volume of s l a g decreases t o h a l f of the stoker i n c i n e r a t o r ash, thus making the land s e r v i c e a b l e f o r a longer p e r i o d . I t cannot be denied that the processing cost of the NSC system i s a l i t t l e higher, because of i t s need f o r coke and limestone. Despite t h a t , the p y r o l y s i s and melting system i s economical when advantages (2) and (3) are d e s i r e d o r when u n d e r i r a b l e combustible refuse have t o be processed. RECEIVED

November 16, 1979.


Thermal Conversion of Solid Wastes and Biomass - ACS Publications

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